The present invention relates to methods and apparatus for applying a layer of a resist, e.g., a photoresist, to both sides of dual-sided substrates, e.g., disk-shaped substrates. The invention finds particular utility in performing resist coating of substrates as part of manufacturing processing of hard disk magnetic and/or magneto-optical recording media, e.g., for servo patterning, protective layer formation, etc.
Spin coating of wafer-shaped substrates or workpieces is a widely utilized process in the manufacture of semiconductor integrated circuit (xe2x80x9cICxe2x80x9d) devices for applying thin, uniform thickness layers of a coating material, e.g., a photoresist, to the wafer surfaces as part of photolithographic patterning of the IC component devices, interconnections, etc., and is increasingly employed as part of the manufacturing process of disk-shaped magnetic and/or magneto-optical (xe2x80x9cMOxe2x80x9d) recording media, such as hard disks, for patterning the surfaces of such media, as for example, in the formation of servo patterns therein by means of imprint lithographic techniques.
A typical spin coating apparatus according to the conventional art is schematically illustrated in the cross-sectional view of FIG. 1, wherein reference numeral 1 designates a disk-shaped rotatable table or vacuum chuck, supported by a rotatable shaft 2 perpendicular to the plane of table 1, the latter being connected to motor 3 for rotation about a central axis. Wafer 11 is fixed to the surface of table or vacuum chuck 1 by means of suction ports (not shown in the drawing for simplicity).
Reference numeral 4 indicates a process bowl or cup surrounding rotatable table or vacuum chuck 1, the bottom of which includes at least one exhaust port 5 for removal of superfluous (i.e., excess) resist (or other coating material) which is scattered about during the spin coating process due to centrifugal force; reference numeral 6 indicates a plate or flange for regulating the air currents flowing in the process bowl or cup 4 in order to enhance coating thickness uniformity; and reference numeral 7 indicates an exhaust port for connection to an exhaust source; reference numeral 8 designates a coating material dispensing nozzle, operatively connected via feed tube or conduit 9 to a source 10 of a coating material, e.g., a photoresist.
In operation of the above-described spin coating apparatus, the coating material, e.g., a photoresist, is dispensed from nozzle 8 of source 10 onto the surface of wafer 11 as the wafer is spun by means of rotatable chuck 1. The spinning of the wafer distributes the photoresist over the surface of the wafer and exerts a shearing force that separates excess photoresist from the wafer and evaporates solvent therefrom, thereby providing a thin, smooth, uniform thickness layer of photoresist on the surface of the wafer.
More specifically, and with reference to FIG. 2, the spin coating process as described above comprises 3 distinct process steps or phases, as follows:
1. Resist spin-onxe2x80x94generally the substrate or workpiece, in the form of an annularly-shaped disk, spins at a low spindle speed during this phase, e.g., about 500 rpm, with a resist dispensing nozzle at the end of a movable arm initially positioned facing the inner diameter (xe2x80x9cIDxe2x80x9d) of the disk. The nozzle/arm assembly dispenses the coating material, e.g., a resist such as a polymethylmethacrylate (xe2x80x9cPMMAxe2x80x9d) or other photo-sensitive resist, onto the top surface of the disk at a controlled rate and duration. The slow spindle speed ensures that the resist is uniformly distributed from the ID to the outer diameter (xe2x80x9cODxe2x80x9d) of the disk, and the flow rate of the resist is adjusted so as to provide a sufficient amount of resist during the spreading process.
2. Resist spin-offxe2x80x94in order to facilitate uniform spreading of the resist, a high spindle speed (e.g., greater than 1,000 rpm) spin-off step is performed in the next phase to remove superfluous (i.e., excess) resist. Conventional spin coating apparatus, such as illustrated in FIG. 1, therefore include a vacuum exhaust system which operates at the backside of the disk to ensure removal of the excess resist without either re-depositing resist material on the top surface of the disk or other critical equipment components located above the disk.
3. Edge bead removal (not shown in FIG. 2)xe2x80x94subsequent to resist spin-off at high spindle speed, the resist-coated disk is subjected to solvent cleaning at the OD disk edge for edge bead removal and a backside wash in order to ensure that the disk OD does not retain a ring (i.e., edge bead) of accumulated resist at the top edge surface; the backside wash protects against undesired resist contamination of the back side (i.e., bottom) of the disk.
In order to facilitate resist coating of both sides of a disk-shaped substrate or workpiece (i.e., xe2x80x9cdual-sidedxe2x80x9d coating) according to conventional automated manufacturing practices utilizing typical prior art spin coating stations, e.g., as shown in FIG. 1, a disk inversion (or xe2x80x9cflippingxe2x80x9d) station must be provided intermediate separate first and second spin coating stations for sequential coating of the top and bottom disk surfaces. While such an arrangement can be fairly readily implemented, this approach entails several disadvantages, as follows:
1. a certain amount of resist material applied to a first (e.g., top) surface of the disk at a first spin coating station, will inevitably flow to the second surface of the disk, i.e., the bottom or backside surface, which resist flow is problematic at at least the second spin coating station;
2. the area (xe2x80x9cequipment footprintxe2x80x9d) occupied by the overall spin coating station is increased due to the requirement for first and second spin coating stations;
3. excessive equipment downtime due to malfunctioning, maintenance, etc., of the first and second spin coating stations and intermediate substrate (e.g., disk) flipping station; and
4. increased equipment cost due to the necessity for providing the second spin coating station and the substrate flipping station.
In view of the above-described drawbacks and disadvantages associated with conventional spin coating methodology when utilized for coating both sides of a dual-sided substrate, as in the case of disk-shaped magnetic and MO recording media such as hard disks, dip coating techniques in which a vertically oriented substrate is immersed in and removed from a bath of photoresist solution in an open container, have been considered as a potentially desirable substitute therefor. Specifically, such dip coating process/apparatus can be readily implemented for coating both sides of two-sided substrates, with an attendant reduction in photoresist loss which minimizes photoresist usage. However, conventional dip coating techniques utilizing open dip cup apparatus (described in more detail below) incur several disadvantages and drawbacks, as follows:
1. Increase in viscosity over timexe2x80x94The photoresist solution, composed of a polymeric photoresist material and at least one solvent therefor, is contained in a tank or vessel (xe2x80x9cdip cupxe2x80x9d) and exposed to the ambient atmosphere, i.e., air. As a consequence of the continuous exposure of the photoresist solution to air, evaporation of the solvent occurs, resulting in an increase in the viscosity of the photoresist solution over time. The increase in viscosity in turn leads to an increase in the thickness of the photoresist coating formed on the substrate surfaces. However, consistent photoresist coating thickness is vital for obtaining acceptable products or results when utilized as part of a manufacturing process, e.g., as a step in the formation of servo-patterned magnetic and MO recording media utilizing imprint lithography of resist-coated substrates. Specifically, a variation, i.e., an increase, in resist layer thickness is problematic in that the latter is a key process variable or parameter in servo pattern formation via imprint lithography utilizing etching or implantation processing for pattern generation in the media surfaces. For example, if the surface patterning is performed by etching utilizing the photoresist layer in patterned form as a selective masking layer, a photoresist layer which is too thick will result in an insufficiently deep etched pattern. As a consequence of the reduced etch depth, the desired spacing between the transducer head and the base of the etched pit will not be obtained, resulting in a reduction in the signal-to-noise ratio (xe2x80x9cSNRxe2x80x9d). Attentively, if the media surface is patterned by implantation processing utilizing a patterned (i.e., embossed or imprinted) resist layer of varying thickness as an implantation mask, the increased thickness of the photoresist layer arising from the increase in viscosity of the photoresist solution increases the required penetration distance of the implanted species, which in turn reduces the magnitude of the desired alteration of magnetic properties of the selectively implanted areas of the substrate surface forming the desired pattern. Again, the result is the SNR of the medium is disadvantageously reduced.
2. Incorporation of Particulatesxe2x80x94A problem frequently associated with photoresist dip coating processes is the incorporation of particulate matter in the photoresist solution. Specifically, the open dip cup utilized for containing the photoresist solution applied to the substrate surfaces by dipping the substrate thereinto, is highly susceptible to contamination by various types of particulate matter. In instances where the photoresist solution is contaminated with particles, debris, etc., the latter are readily transferred to subsequent substrates immersed in the contaminated photoresist solution in the dip cup. In such event, it becomes necessary to terminate the dip coating process, discard, and then replace the entire volume of photoresist solution in the dip cup. As a consequence, contamination of the photoresist solution with particles, debris, etc., can entirely eliminate the benefit of low photoresist consumption afforded by the dip coating process.
In view of the above-described drawbacks and disadvantages inherent in the open cup dip coating approach for applying a layer of a coating material, e.g., a photoresist layer, to both sides of dual-sided substrates, e.g., disk-shaped substrates such as utilized in the manufacture of semiconductor integrated circuit devices and magnetic and/or MO recording media, there exists a clear need for improved means and methodology for performing dip coating of dual-sided substrates such as semiconductor wafers and disks for magnetic and/or MO recording media. More specifically, there exists a need for an improved means and methodology for simultaneously dip coating both sides of dual-sided substrates in an open dip cup coating station, whereby each of the above-described drawbacks and disadvantages accruing from the use of conventional open dip cup resist coating stations is avoided.
The present invention addresses and solves problems, difficulties, drawbacks, and disadvantages associated with the conventional open dip cup coating station approach for dip coating of a resist material on both sides of dual-sided substrates, e.g., semiconductor wafers and disk-shaped substrates employed in the manufacture of hard disk magnetic and/or MO recording media, the drawbacks and disadvantages including resist thickness variation/increase, particle contamination, downtime, and high resist. usage/waste, while maintaining full compatibility with all aspects of conventional automated manufacturing technology, e.g., for semiconductor IC and recording media manufacture. Further, the means and methodology afforded by the present invention enjoy diverse utility in spin coating of a variety of materials on a number of different types of substrates and workpieces.
An advantage of the present invention is an improved open dip cup apparatus for dip coating a layer of a resist material on a surface of a substrate.
Another advantage of the present invention is an improved apparatus for simultaneously dip coating a layer of a resist material on the oppositely facing major surfaces of a disk-shaped substrate for a magnetic or magneto-optical recording medium.
A further advantage of the present invention is an improved method of performing dip coating of a layer of a resist material on a surface of a substrate.
Still another advantage of the present invention is an improved method of performing simultaneous dip coating of a layer of a resist material on the oppositely facing major surfaces of a disk-shaped substrate for a magnetic or magneto-optical recording medium.
Yet another advantage of the present invention is an improved method and apparatus for performing open dip coating of substrates in a continuous process while maintaining the viscosity of the dip coating liquid constant at a desired level and removing particulate matter therefrom.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by an improved apparatus for performing dip coating of a layer of a resist material on at least one surface of a substrate, comprising:
a dip coating vessel having an interior space adapted for containing therein a liquid for dip coating of a substrate, the dip coating liquid comprising a solution of the resist material in a solvent, the vessel being open at the top thereof;
a substrate mounting means for introducing into and withdrawing a substrate from the interior space of the dip coating vessel via the open top; and
a viscosity control system for continuously monitoring and maintaining the viscosity of a dip coating liquid supplied to the dip coating vessel at a predetermined value.
According to an embodiment of the present invention, the viscosity control system includes a recirculation loop for continuously or periodically recirculating the dip coating liquid in the dip coating vessel; wherein, according to a particular embodiment of the invention, the recirculation loop includes a reservoir for the dip coating liquid, with an inlet conduit connected between the reservoir and the dip coating vessel for supplying dip coating liquid from the reservoir to the dip coating vessel, and an outlet conduit connected between the dip coating vessel and the reservoir for returning dip coating liquid from the dip coating vessel to the reservoir.
In accordance with certain embodiments of the present invention, the recirculation loop provides periodic recirculation of the dip coating liquid in the dip coating vessel and comprises a bypass conduit for periodically diverting, thus interrupting, flow of the dip coating liquid between the reservoir and the dip coating vessel; wherein the recirculation loop provides recirculation of the dip coating liquid in the dip coating vessel only when a substrate is immersed in the dip coating liquid in the dip coating vessel and includes a pair of 3-way flow valves for flowing the dip coating liquid through the bypass conduit in response to a signal provided by the substrate mounting means.
According to embodiments of the present invention, the recirculation loop further includes a pump connected to the inlet conduit for recirculating the dip coating liquid; and the recirculation loop further includes a filter connected to the inlet conduit for removing particulate matter from the dip coating liquid.
Embodiments of the present invention include providing the recirculation loop as including a device for continuously measuring the viscosity of the dip coating liquid in the reservoir and a solvent dispensing system for supplying the solvent for the resist material to the reservoir in response to the measured viscosity.
According to certain embodiments of the present invention, the solvent dispensing system includes a tank for containing the solvent and a conduit between the solvent tank and the reservoir for supplying a flow of solvent from the solvent tank to the reservoir; and the solvent dispensing system further includes a valve for controlling the flow of solvent in the conduit between the solvent tank and the reservoir, and valve flow control means responsive to the measured viscosity for controlling the solvent flow and thereby maintaining the predetermined viscosity of the dip coating liquid in the reservoir and in the dip coating vessel.
In accordance with further embodiments of the present invention, the reservoir further includes agitator means for uniformly mixing solvent supplied by the solvent dispensing system with the dip coating liquid in the reservoir; and the substrate mounting means includes means for vertically mounting a disk-shaped substrate comprising a pair of oppositely facing major surfaces to be simultaneously dip coated, and means for rotating the disk-shaped substrate about a central axis.
Another aspect of the present invention is an improved method of performing dip coating of a layer of a resist material on a surface of a substrate, comprising steps of:
(a) providing a dip coating vessel having an interior space containing therein a liquid for dip coating, the dip coating liquid comprising a solution of the resist material in a solvent, the dip coating vessel being open at the top thereof;
(b) providing a substrate having a surface, immersing the substrate in the dip coating liquid in the dip coating vessel via the open top, and withdrawing the substrate from the dip coating vessel via the open top, thereby forming a layer of the resist material on the substrate surface; and
(c) monitoring and maintaining the viscosity of the dip coating liquid supplied to the dip coating vessel at a predetermined value.
In accordance with embodiments of the present invention, step (b) comprises providing and immersing a vertically oriented, disk-shaped substrate having a pair of opposed major surfaces while rotating the disk-shaped substrate about a central axis, thereby simultaneously forming a layer of the photoresist material on each of the pair of surfaces; and
step (c) comprises providing a continuous viscosity control system including a circulation loop for continuously or periodically recirculating the dip coating liquid in the dip coating vessel.
According to embodiments of the present invention, step (c) comprises providing a recirculation loop including a reservoir for the dip coating liquid, with an inlet conduit connected between the reservoir and the dip coating vessel for supplying dip coating liquid from the reservoir to the dip coating vessel, and an outlet conduit connected between the dip coating vessel and the reservoir for returning dip coating liquid from the dip coating vessel to the reservoir.
In accordance with certain embodiments of the present invention, step (c) comprises providing a recirculation loop for periodically recirculating the dip coating liquid in the dip coating vessel, the recirculation loop comprising a bypass conduit for periodically diverting, thus interrupting, flow of the dip coating liquid between the reservoir and the dip coating vessel; wherein step (c) comprises providing a recirculation loop for recirculating the dip coating liquid in the dip coating vessel only when a substrate is immersed in the dip coating liquid in the dip coating vessel, and the recirculation loop includes a pair of 3-way flow control valves for flowing the dip coating liquid through the bypass conduit in response to a signal provided by the substrate mounting means.
According to embodiments of the present invention, step (c) further comprises providing a recirculation loop including a pump connected to the inlet conduit for recirculating the dip coating liquid and a filter connected to the inlet conduit for removing particulate matter from the dip coating liquid, and step (c) further comprises providing a recirculation loop including a device for continuously measuring the viscosity of the dip coating liquid in the reservoir and a solvent dispensing system for supplying the solvent for the resist material to the reservoir in response to the measured viscosity.
In a particular embodiment of the present invention, step (c) comprises providing a solvent dispensing system including a tank for containing the solvent and a conduit between the solvent tank and the reservoir for supplying a flow of solvent from the solvent tank to the reservoir; and according to certain embodiments of the invention, a solvent dispensing system is provided which further comprises a valve for controlling the flow of solvent in the conduit between the solvent tank and the reservoir, and valve flow control means responsive to the measured viscosity for controlling the solvent flow and thereby maintaining the predetermined viscosity of the dip coating liquid in the reservoir and in the dip coating vessel.
In accordance with a further embodiment of the present invention, step (c) further comprises providing the reservoir with agitator means for uniformly mixing solvent supplied by the solvent dispensing system with the dip coating liquid in the reservoir.
According to an embodiment of the present invention having particular utility in the manufacture of recording media, step (b) comprises providing a disk-shaped substrate for a hard disk magnetic or magneto-optical (MO) recording medium and the resist material is a photoresist.
Yet another aspect of the present invention is an improved apparatus for performing dip coating of a layer of a resist material on at least one surface of a substrate, comprising:
an open cup dip coating vessel having an interior space for containing therein a dip coating liquid; and
means for monitoring and maintaining the viscosity of the dip coating liquid supplied to the dip coating vessel at a predetermined value.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.